Process for producing cobalt metal powder from nickel-cobalt sulphides

Abstract

A process for producing cobalt metal powder from nickel-cobalt sulphides wherein said nickel-cobalt sulphides are leached in an ammoniacal ammonium sulphate solution under an elevated pressure of an oxygen bearing gas, at a temperature of at least 80° C., with an effective ammonia to metals mole ratio in the range of 5:1 to 6.5:1 to oxidize the nickel and cobalt sulphides to sulphates, and to produce an ammoniacal leach liquor in which dissolved cobalt is predominantly in the (III) oxidation state, and an ammoniacal ammonium sulphate leach residue containing a cobalt (III) hexammine sulphate-calcium sulphate double salt. The improvement comprises repulping the ammoniacal ammonium sulphate leach residue, containing the cobalt (III) hexammine sulphate-calcium sulphate double salt, with a solution containing an effective amount of ammonium carbonate to dissolve the cobalt (III) hexammine sulphate in the repulp leach liquor and precipitate calcium carbonate; and separating the repulp leach liquor containing cobalt (III) hexammine sulphide from the repulp leach residue containing calcium carbonate.

I claim:  
     
       1. In a process for producing cobalt metal powder from nickel-cobalt sulphides comprising leaching said nickel-cobalt sulphides in an ammoniacal ammonium sulphate solution under an elevated pressure of an oxygen bearing gas, at a temperature of at least 80° C., with an effective ammonia to metals mole ratio in the range of 5:1 to 6.5:1 to oxidize the nickel and cobalt sulphides to sulphates, and to produce an ammoniacal ammonium sulphate leach liquor in which dissolved cobalt is predominantly in the (III) oxidation state, and an ammoniacal ammonium sulphate leach residue containing a cobalt (III) hexannmine sulphate-calcium sulphate double salt, separating the ammoniacal ammonium sulphate leach liquor from the ammoniacal ammonium sulphate leach residue, saturating the ammoniacal ammonium sulphate leach liquor with an effective amount of anydrous ammonia and cooling the ammoniated leach liquor to below 50° C. to precipitate the triple salt of cobalt (III) hexammine supbate, nickel (II) hexammine sulphate and ammonium sulphate, recovering the precipitated triple salt from the leach liquor, repulping the triple salt with an effective amount of water to selectively leach nickel(II) hexammine sulphate and to produce a crystalline cobalt (III) hexammine sulphate with a Co:Ni ratio of at least 100:1 and a nickel enriched leach liquor, dissolving the cobalt (III) hexammine sulphate in hot ammonium sulphate solution, and cooling the solution to precipitate recrystallized cobalt (III) hexammine sulphate having a Co:Ni ratio of at least about 1000:1 and treating the recrystallized cobalt (III) hexammine sulphate to produce cobalt metal therefrom, the improvement comprising: 
       repulping said ammoniacal anunonium sulphate leach residue, containing the cobalt (III) hexammine sulphate-calcium sulphate double salt, with a solution containing an effective amount of ammonium carbonate to dissolve the cobalt (III) hexammine sulphate in the repulp leach liquor and precipitate calcium carbonate; and  
       separating the repulp leach liquor containing cobalt (III) hexammine sulphate from the repulp leach residue containing calcium carbonate.  
     
     
       2. The process as set forth in claim  1  wherein said effective amount of ammonium carbonate ranges between about 10 g/L to 100 g/L. 
     
     
       3. The process as set forth in claim  1  wherein the separated repulp leach liquor containing said cobalt (III) hexammine sulphate is recycled to said repulping. 
     
     
       4. The process as set forth in claim  3  wherein said effective amount of anuonium carbonate ranges between about 10 g/L to 100 g/L. 
     
     
       5. The process as set forth in claim  3  wherein said repulp leach liquor containing said cobalt (III) hexamine sulphate is recycled to said triple salt precipitation. 
     
     
       6. The process as set forth in claim  5  which further comprises treating the recrystallized cobalt (III) hexammine sulphate by dissolution in hot ammonium sulphate solution, treating the said hot ammonium sulphate solution containing dissolved cobalt (III) hexammme sulphate with an effective amount of cobalt powder to reduce Co(III) to Co(II) and treating the said hot ammonium sulphate solution containing Co(II) with hydrogen to produce cobalt powder therefrom. 
     
     
       7. A process as set forth in claim  6  wherein the ammoniacal leach liquor is saturated with an effective amount of ammonia by adding anhydrous ammonia or a solution of ammonium hydroxide to provide about 170 to 190 g/L tam titratable ammonia, in which the ammoniacal leach liquor contns about 150 to 250 g/L ammonium sulphate and in which the saturated leach liquor is cooled to a temperature in the range of 20° C. to 40° C. 
     
     
       8. A process as set forth in claim  7  wherein the precipitated triple salt is repulped with an effective amount of water at a rate to maintain the titratable ammonia concentration at about 100 to 120 g/L. 
     
     
       9. A process as set forth in claim  8  wherein the precipitated triple salt is repulped with an effective amount of water at a rate effective to maintain the titratable ammonia concentration at about 100 to 120 g/L and wherein the solution is maintained at a temperature in the range of about 20° to 40° C.